Exploring the Reactivity of Donor-Stabilized Phosphenium Cations: Lewis Acid-Catalyzed Reduction of Chlorophosphanes by Silanes

Abstract

Phosphane-stabilized phosphenium cations react with silanes to effect either reduction to primary or secondary phosphanes, or formation of P-P bonded species depending upon counteranion. This operates for in situ generated phosphenium cations, allowing catalytic reduction of P(III)-Cl bonds in the absence of strong reducing agents. Anion and substituent dependence studies have allowed insight into the competing mechanisms involved.

Kinetically Stabilized Diarylpnictogenium Ions

“…Unless otherwise noted, NMR spectra were recorded at room temperature on Bruker Avance Neo 600 MHz spectrometers. 1 H, 13 C { 1 H}, 11 B and 19 F, NMR spectra are reported on the δ scale (ppm) and are referenced against SiMe 4 , BF 3 • Et 2 O (15 % in CDCl 3 ) and CFCl 3 , respectively. 1 H and 13 C{ 1 H} chemical shifts are reported relative to the residual peak of the solvent (CDHCl 2 : 5.32 ppm, for CD 2 Cl 2 ) in the 1 H NMR spectra, and to the peak of the deuterated solvent (CD 2 Cl 2 : 53.84 in the 13 C{ 1 H} NMR spectra.…”

“…Unlike those, pnictogenium ions are also strong electrophiles, which can be attributed to the positive charge that attracts any nucleophile present. Consequently, the vast majority of phosphenium ions, [R 2 P] + , [2–33] arsenium ions, [R 2 As] + , [34–51] stibenium ions, [R 2 Sb] +[52–59] and bismuthenium ions, [R 2 Bi] + , [60–72] reported in the literature are either affected by ion pairing or stabilized by electron‐rich ligands or substituents, which inter‐ or intramolecularly fill the vacant p‐orbital. These electronically stabilized pnictogenium ions often have a dramatically reduced Lewis acidity and cannot be regarded as genuine 6 VE species as they fulfill or even exceed the octet rule.…”

“…3J( 1 H-1 H) = 8 1 J( 13 C-19 F) = 241 Hz, C 6 F 5 ), 143.91 (s, C25), 143.31 (s, C27), 138.81 (d, br, 1 J( 13 C-19 F) = 245 Hz, C 6 F 5 ), 137.77 (s, C16), 137.67 (s, C1), 136.90 (d, br, 1 J( 13 C-19 F) = 224 Hz, C 6 F 5 ), 136.03 (s, C24), 134.74 (s, C15), 134.05 (s, C26), 132.47 (s, C20), 132.42 (s, C19), 131.22 (s, C12), 128.71 (s, C13), 128.55 (C18), 125.54 (s, C11), 123.94 (s, C21), 122.01 (s, C14), 118.92 (s, C4), 64.43 (s, C5), 51.66 (s, C6), 46.49 (s, C7), 33.70 (s, C9), 32.94 (s, C8), 30.40 (s, C29), 26.51 (s, C28), 22.82 (s, C30).19 F NMR (565 MHz, CD 2 Cl 2 ): δ =-133.09 (br, 8F, o-C 6 F 5 ), À 163.70 (t, 3 J( 19 F-19 F) = 20 Hz, 4F, p-C 6 F 5 ), À 167.54 (t, br, 3 J( 19 F-19 F) = 20 Hz, 8F, m-C 6 F 5 ).…”

Reversible Silylium Transfer between P‐H and Si‐H Donors

“…The Lewis acidity of free phosphenium ions is well established, [7i, 14, 15] and recently examples of electrophilic Si‐H abstraction by phosphenium ions have been reported [2b,f, 7g, 16] . However, despite evidence for the electrophilicity of metal‐coordinated phosphenium ligands, [17, 18] their Lewis acidity has not been explicitly assessed, and their interactions with silanes remain unexplored.…”

9-BBN and chloride catalyzed reduction of chlorophosphines to phosphines and diphosphines

“…In 2018, Clark and coworkers used GaCl 3 or AlCl 3 to mediate P-P bond formation from R 2 PCl in the presence of silane at 100 1C, although these reactions were slow requiring 5-7 days. 23 Very recently Hering-Junghans and coworkers described the reduction of Mes 2 PX and Ph 2 PX to the corresponding P 2 R 4 products in the presence of catalytic PEt 3 and sacrificial Zn reductant. 24 In this manuscript we employ 9-BBN or chloride ion as catalysts to effect the reduction of chlorophosphines in the presence of silane.…”